[Decompilation] [th04] Bullets: Clipping and pre-spawn hit test

First place to confirm the hitbox of both the 8×8 pellets and the 16×16
sprite bullets!

Well, "hitbox". It's really more of a kill delta of 8×8 pixels between
the center points of a bullet and the player. You can distribute these
pixels to any combination of bullet and player "hitboxes" that make up
8×8. 4×4 around both the player and bullets? 1×1 for bullets, and 8×8
for the player? All equally valid… or perhaps none of them, once you
keep in mind that other entity types might have different kill deltas,
which turns the concept of a "hitbox" into just a confusing abstraction.

Part of P0150, funded by Blue Bolt.

th01/math/overlap.hpp

@@ -22,3 +22,8 @@
 
 #define overlap_xy_xywh_le_ge(x1, y1, x2, y2, w2, h2) \
 	overlap_xy_ltrb_le_ge(x1, y1, x2, y2, (x2 + w2), (y2 + h2))
+
+#define overlap_points_wh_fast(p1, p2, p1_w, p1_h) ( \
+	((unsigned int)((p1.x - p2.x) + (p1_w / 2)) <= (p1_w)) && \
+	((unsigned int)((p1.y - p2.y) + (p1_h / 2)) <= (p1_h)) \
+)

th02/main/player/player.h

@@ -1,6 +1,8 @@
 #define PLAYER_W 32
 #define PLAYER_H 48
 
+extern bool player_is_hit;
+
 // Grants invincibility when >0. Decrements by 1 each frame in that case.
 // In TH02, this works independently from [player_invincible_via_bomb].
 extern unsigned char player_invincibility_time;

th04/main/bullet/add.cpp

@@ -428,3 +428,33 @@ unsigned char pascal near bullet_patnum_for_angle(unsigned char angle)
 		((angle + (ANGLE_PER_SPRITE / 2) - 1) & (0x80 - 1)) / ANGLE_PER_SPRITE
 	);
 }
+
+bool near bullet_template_clip(void)
+{
+	if(
+		(bullet_clear_time > 0) &&
+		(bullet_clear_time <= (BMS_DECAY_FRAMES + 1))
+	) {
+		return true;
+	}
+	// Also applies to 8×8 pellets, because why wouldn't you combine both
+	// cases. #goodcode
+	if(!playfield_encloses_point(
+		bullet_template.origin, BULLET16_W, BULLET16_H
+	)) {
+		return true;
+	}
+	if(overlap_points_wh_fast(
+		bullet_template.origin,
+		player_pos.cur,
+		BULLET_KILLBOX_W,
+		BULLET_KILLBOX_H
+	)) {
+		player_is_hit = true;
+		return true;
+	}
+	if(!group_fixedspeed) {
+		bullet_template_speedtune_for_playperf();
+	}
+	return false;
+}

th04/main/bullet/bullet.hpp

@@ -91,6 +91,11 @@ struct bullet_t {
 #define BULLET16_W 16
 #define BULLET16_H 16
 
+// Symmetrical around the center point of each bullet, and treated in relation
+// to a 1×1 "hitbox" around the player's center point.
+static const subpixel_t BULLET_KILLBOX_W = TO_SP(8);
+static const subpixel_t BULLET_KILLBOX_H = TO_SP(8);
+
 #if GAME == 5
 # define PELLET_COUNT 180
 # define BULLET16_COUNT 220

th04/main032.cpp

@@ -11,6 +11,7 @@ extern "C" {
 #include "planar.h"
 #include "master.hpp"
 #include "th01/math/subpixel.hpp"
+#include "th01/math/overlap.hpp"
 #include "th04/math/motion.hpp"
 #include "th04/math/randring.h"
 #include "th04/math/vector.hpp"

th04_main.asm

@@ -28230,57 +28230,7 @@ main_033_TEXT	segment	byte public 'CODE' use16
 	_bullet_template_speedtune_for_pl procdesc near
 	BULLET_PATNUM_FOR_ANGLE procdesc pascal near \
 		angle:byte
-
-; =============== S U B	R O U T	I N E =======================================
-
-; Attributes: bp-based frame
-
-sub_1D230	proc near
-		push	bp
-		mov	bp, sp
-		cmp	_bullet_clear_time, 0
-		jbe	short loc_1D241
-		cmp	_bullet_clear_time, 17
-		jbe	short loc_1D282
-
-loc_1D241:
-		cmp	_bullet_template.BT_origin.x, (-8 shl 4)
-		jle	short loc_1D282
-		cmp	_bullet_template.BT_origin.x, ((PLAYFIELD_W + 8) shl 4)
-		jge	short loc_1D282
-		cmp	_bullet_template.BT_origin.y, (-8 shl 4)
-		jle	short loc_1D282
-		cmp	_bullet_template.BT_origin.y, ((PLAYFIELD_H + 8) shl 4)
-		jge	short loc_1D282
-		mov	ax, _bullet_template.BT_origin.x
-		sub	ax, _player_pos.cur.x
-		add	ax, (4 shl 4)
-		cmp	ax, (8 shl 4)
-		ja	short loc_1D286
-		mov	ax, _bullet_template.BT_origin.y
-		sub	ax, _player_pos.cur.y
-		add	ax, (4 shl 4)
-		cmp	ax, (8 shl 4)
-		ja	short loc_1D286
-		mov	_player_is_hit, 1
-
-loc_1D282:
-		mov	al, 1
-		pop	bp
-		retn
-; ---------------------------------------------------------------------------
-
-loc_1D286:
-		cmp	_group_fixedspeed, 0
-		jnz	short loc_1D290
-		call	_bullet_template_speedtune_for_pl
-
-loc_1D290:
-		mov	al, 0
-		pop	bp
-		retn
-sub_1D230	endp
-
+	_bullet_template_clip procdesc near
 
 ; =============== S U B	R O U T	I N E =======================================
 
@@ -28313,7 +28263,7 @@ bullets_add_regular_raw	proc near
 ; ---------------------------------------------------------------------------
 
 loc_1D2D5:
-		call	sub_1D230
+		call	_bullet_template_clip
 		or	al, al
 		jnz	loc_1D3BB
 		mov	[bp+@@spawn_state], BSS_GRAZEABLE
@@ -28436,7 +28386,7 @@ bullets_add_special_raw	proc near
 		sub	sp, 4
 		push	si
 		push	di
-		call	sub_1D230
+		call	_bullet_template_clip
 		or	al, al
 		jnz	loc_1D48A
 		mov	[bp+@@spawn_state], 0

th05_main.asm

@@ -10388,7 +10388,7 @@ sub_15AAA	endp
 ; =============== S U B	R O U T	I N E =======================================
 
 
-sub_15C36	proc near
+_bullet_template_clip	proc near
 		cmp	_bullet_clear_time, 0
 		jz	short loc_15C47
 		cmp	_bullet_clear_time, 17
@@ -10430,7 +10430,7 @@ loc_15C81:
 loc_15C91:
 		mov	al, 0
 		retn
-sub_15C36	endp
+_bullet_template_clip	endp
 
 ; ---------------------------------------------------------------------------
 
@@ -10463,7 +10463,7 @@ locret_15CE4:
 ; ---------------------------------------------------------------------------
 
 loc_15CE5:
-		call	sub_15C36
+		call	_bullet_template_clip
 		or	al, al
 		jnz	short locret_15CE4
 		push	si